The long term evolution-advanced (LTE-A) project of the third generation partnership Project (3GPP) is working towards enhancements of the LTE program. For example, the LTE-A project anticipates the use of peak data rates of 0.5 Gbps in the uplink (UL) direction and 1 Gbps in the downlink (DL) direction. In order to achieve these data rates, UL multiple input/multiple output (MIMO) is being considered for the LTE-A project.
FIG. 1 shows an overview of an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN) 100 in accordance with the prior art. As shown in FIG. 1, E-UTRAN 100 includes three eNodeBs (eNBs) 102, however, any number of eNBs may be included in E-UTRAN 100. The eNBs 102 are interconnected with each other by means of an X2 interface 108. The eNBs 102 are also connected by means of an S1 interface 106 to the Evolved Packet Core (EPC) 104 that includes a Mobility Management Entity (MME) 108 and a Serving Gateway (S-GW) 110.
FIG. 2 shows an LTE user-plane protocol stack 200 in accordance with the prior art. The protocol stack 200 is located in a WTRU 210 and includes the packet data control protocol (PDCP) 202, the radio link control (RLC) 204, the medium access control (MAC) 206 and the physical layer (PHY) 208. The protocol stack 200 may also reside in an eNB (not shown).
FIG. 3 shows an LTE control plane protocol stack 300 of the WTRU 210 of FIG. 2. The control plane protocol stack 300 includes the non-access stratum (NAS) 302 and a radio resource control (RRC) 304. Also included are the PDCP 306, RLC 308 and MAC 310, which together form the layer 2 sublayer 312.
Logical channel prioritization is a procedure that is performed for each new transmission by a transmitting entity. The transmitting RRC entity controls the scheduling of UL data by giving each logical channel a priority. A higher priority value indicates a lower actual priority level. Additionally, each logical channel is given a prioritized bit rate (PBR).
The RRC of a wireless transmit receive unit (WTRU) may perform the logical channel prioritization procedure. FIG. 4 shows a logical channel prioritization method 400 in accordance with the prior art. At step 402 the WTRU allocates resources to the logical channels. The WTRU, at step 404 allocates resources to the logical channels in a decreasing priority order up to a value such that on average, the served data rate for radio bearers that have data for transmission equals the configured PBR for the radio bearer. If the PBR of a radio bearer is set to “infinity”, the WTRU allocates resources for all the data that is available for transmission on the radio bearer before meeting the PBR of the lower priority radio bearers. At step 406 the WTRU, if any resources remain, serve all the logical channels in a strict decreasing priority order until either the data for that logical channel or the UL grant is exhausted, whichever comes first.
For the method 400 shown in FIG. 4, the WTRU may follow certain rules. For example, the WTRU should not segment a radio link control (RLC) service data unit (SDU), or partially transmitted SDU or retransmitted RLC protocol data unit (PDU), if the whole SDU, partially transmitted SDU or retransmitted RLC PDU fits into the remaining resources. Further, if the WTRU segments an RLC SDU from the logical channel, it may maximize the size of the segment to fill the grant as much as possible. Also, the WTRU may use as much data as it can to fill the grant, in general. However, if the remaining resources require the WTRU to segment an RLC SDU with size smaller than a certain number of bytes or smaller than the L2 header size, the WTRU may use padding to fill the remaining resources instead of segmenting the RLC SDU and sending the segment.
Logical channels configured with the same priority are served equally by the WTRU. Medium access control (MAC) control elements for buffer status reporting, with exception of padding BSR, have higher priority than user plane logical channels. At a serving cell change, the first UL dedicated control channel (DCCH) MAC SDU to be transmitted in the new cell has higher priority than MAC control elements for BSR.
With the introduction of UL MIMO in LTE-advanced, enhanced MAC logical channel prioritization and multiplexing mechanisms may be needed to handle multiple transport blocks (TBs) within the same transmission time interval (TTI).